There exist in today's market imaging devices capable of reading documents such as ID cards, drivers license, business cards, passports, medical cards and the like. In imaging devices that include an imaging sensor array, based on technologies such as a CCD or CMOS, it is required to illuminate the imaged document. It is desired that the illumination will be of high intensity and substantially uniform, in order to obtain a substantially true image of the imaged document.
The document is typical place on the surface of a substantially flat and substantially transparent panel, typically, with no limitation, made of glass (herein, also referred to as “glass-window”). But the glass surface and the imaged document are also a reflective surface, returning a portion of the incident light rays striking the transparent glass surface. Thereby, the image frame acquired from the imaged document is distorted. An internal light source that directly illuminates the glass-window bring are reflected from the glass surface, thereby forming “hotspots” that distort the uniformity of the illumination of the imaged document, and thereby causing the image of the imaged document not to be a substantially true image of the imaged document.
U.S. Pat. No. 7,911,655 and US patent application 20110128360, by Hatzav et al., provide apparatuses for acquiring digital image frames of one or both sides of identification documents, having an illumination system configuration that reduces the hotspot problem, by disposing the light sources outside the field of view (FOV) of the camera. The hotspot problem is also addressed by Hatzav et al. in U.S. Pat. No. 7,948,665 and U.S. patent application Ser. Nos. 12/393,504 and 13/185,510.
U.S. patent application Ser. No. 13/223,342, by Hatzav et al., filed Sep. 1, 2011, provides an imaging device for imaging documents, wherein the document is directly illuminated from at least two illuminating angles, and wherein the output image frame does not contain hotspots formed as a result of the direct illumination of either of the at least two illuminating angles.
U.S. patent application Ser. No. 13/223,342, in incorporated by reference for all purposes as if fully set forth herein. Reference is now made to FIG. 1 (prior art), a side view illustration of an imaging device 80, according to U.S. patent application Ser. No. 13/223,342, wherein a side wall has been removed for illustration purposes only. Imaging device 80 includes a body 40 enclosing an imaging-optical-chamber 70, a camera 50, two or more clusters of light sources 30, a glass-window 20 and a processor 90. Reference is also made to FIG. 2 (prior art), a perspective view illustration of imaging device 80. It should be noted that in FIGS. 1 and 2, a side wall has been removed for illustration purposes only.
Camera 50 is disposed on the internal surface of a camera wall 55 such that, preferably, the FOV 60 of lens 52 of camera 50 views at least the whole of glass-window 20. Typically, camera wall 55 is disposed opposite to glass-window 20. Typically, clusters of light sources 30 are also disposed on the internal surface of camera wall 55 such that clusters of light sources 30 are not directly viewed by the FOV 60 of camera 50.
The operation of imaging device 80 is explained through an example supported by FIGS. 3a-3d. FIG. 3a depicts an example document 10a, containing 9×9 rectangles arranged in a larger rectangle and separated by white gaps.
The method of the present invention is exemplified, with no limitations, in FIGS. 3b-3d. The two clusters of light sources 30a and 30b are alternately activated, at a preconfigured activation rate. When light source cluster 30a is ON, light source cluster 30b is OFF, and vice versa. Each image frame is subdivided, for example, into two sections, a top section and a bottom section, wherein “top” and “bottom” refer to the image frames (14, 16 and 18), as seen in FIGS. 3b-3c. 
FIG. 3b depicts an example image frame 14 of document 10a, acquired by imaging device 80, wherein a first cluster of light sources 30a is activated, forming a respective hotspots 13a within the bottom section 14b of image frame 14.
Similarly, FIG. 3c depicts an example image frame 16 of document 10a, acquired by imaging device 80, wherein a second cluster of light sources 30b is activated, forming a respective hotspots 13b within the top section 16t of image frame 16.
FIG. 3d depicts an example output image frame 18 of document 10a, composed from portions of the image frames 14 and 16. The acquired image frames are stored in memory, operatively coupled with processor 90. Each pair of the acquired image frame, 14 and 16, includes an image frame section that is clean of hotspots formed by a cluster of light sources 30. In image frame 14 the top section 14t is clean of hotspots formed by a cluster of light sources 30, and in image frame 16 the bottom section 16b is clean of hotspots formed by a cluster of light sources 30. Processor 90 concatenates the top section 14t of image frame 14 onto the bottom section 16b image frame 16, thereby forming a new image frame 18, contains substantially no hotspots.
In prior art imaging device for imaging documents that facilitates imaging both sides of the document (also referred to as a “duplex imaging device” or a “duplex imaging apparatus”), substantially simultaneously, an ejection mechanism is required for removing the document from the duplex imaging device, since the whole document is typically inserted in a slot between two glass windows. The ejection mechanism is typically complex, cumbersome and burdensome the duplex imaging device as a whole.
Prior art duplex imaging devices also take measures to overcome the partial transparency of some documents, such as paper documents, as the illumination of a first side of the document is viewed as direct illumination by the camera set to image the second side of the document. Some prior art attempts to solve this problem provided complex solutions, for example, in U.S. Pat. No. 7,388,691, by Kuo-Jeng Wang.
Thus there is a need for and it would be advantageous to have a duplex imaging apparatus that does not require a complex and cumbersome ejection mechanism for removing the document from the apparatus.